Sealing arrangement for rotary combustion engine

ABSTRACT

A sealing arrangement for the apexes of the rotor of a rotary combustion engine, wherein the inner surface of the peripheral housing, the end walls, and the parts of the seal are of different graduated hardnesses, whereby the seal rapidly wears into a perfect fit and sealing engagement without danger of scoring or abrading the housing.

Unite States Patent 1191 Beutter 1 Jan. 23, 1973 [541 SEALINGARRANGEMENT FOR ROTARY COMBUSTION ENGINE Karl Beutter, l-leilbronn,Germany Assignees: Audi NSU Auto Union Aktiengesellschatt, Neckarsulm;Wankel G.m.b.H., Lindau, Bodensee, Germany Filed: May 20, 1971 Appl.No.2 145,442

Inventor:

[30] Foreign Application Priority Data June 3, 1970 Germany ..P 20 27115.2

US. Cl. ..418/l21, 418/122, 418/178, 418/179 Int. Cl ..F01c 19/02, F0363/00, F046 27/00 Field 01 Search ..418/121, 122,178,179, 113,

[56] References Cited UNITED miss 1min;

3,554,677 1/1971 Zapf et a1. ..4l8/l78 3,263,912 8/1966 Frenzel ..41s179' 3,281,064 10/1966 Springer ..41s 179 3,318,515 5/1967 Jones..4l8/l78 3,608,535 9/1971 Winston et a1. ....41s 17s 3,394,877 7/1968l-lantzsche et al. ..4l8/178 Primary ExaminerCarlton R. Croyle AssistantExaminer.lohn J. Vrablik Attorney-Raymond P. Wallace and Victor D. Behn[57] ABSTRACT A sealing arrangement for the apexes of the rotor of arotary combustion engine, wherein the inner surface of the peripheralhousing, the end walls, and the parts of the seal are of differentgraduated hardnesses, whereby the seal rapidly wears into a perfect titand sealing engagement without danger of scoring or abrading thehousing.

7 Claims, 2 Drawing Figures SEALING ARRANGEMENT FOR ROTARY COMBUSTIONENGINE BACKGROUND OF THE INVENTION This invention relates to an improvedapex sealing means for the rotor of a rotary engine.

There is known in the prior art, as shown by U. S. Pat. No. 3,400,691, athree-piece apex seal for rotary engines, wherein there is a main sealpiece of trapezoidal form and two triangular end pieces, the end piecesmeeting the main piece along diagonal lines passing substantiallythrough the radially outward corners of the assembly. The edge of themain piece sweeps along the surface of the peripheral housing and theedges of the end pieces slide on the inner faces of the side walls ofthe engine. The object of this arrangement is that the length of themain seal piece shall be accommodated between the side walls when theengine is cold, with the end pieces held radially and axially in contactalong their sliding plane lines with the main piece. When the engine ishot and the length of the operating chamber expands, the end pieces areforced radially outward by their spring loading, and also longitudinallyoutward along the inclined planes, thus maintaining sealing contact withthe side walls and at least in part filling the gaps at the comers ofthe main seal piece. If the axial spacing between the side walls variesfrom place to place in the periphery of the engine, as between a hotzone and a relatively cool zone, the triangular end seal pieces aresqueezed in and out as the rotor turns.

The disadvantage of this arrangement is that at times when the axialspacing of the side walls is minimal, because of manufacturingtolerances the corners of the main seal piece may gouge the surface ofthe side walls, or the delicate corners of the seal are rapidly wornoff, permanently enlarging the leakage gap at the corners. At othertimes, when axial spacing of the side walls is greater than the lengthof the seal members in their optimum position, the corners of thetriangular end seal pieces may gouge the peripheral housing surface, oragain, their delicate comers may be rapidly worn down, so that thecorner gap is again enlarged. Also, these difficulties are not duesolely to manufacturing tolerances and to varying engine conditions, butin addition they may arise from uneven wear of the seal parts owing tominute variations in hardness.

SUMMARY The present invention results in optimum sealing over a longperiod of time, and keeps as small as possible the wear of the innersurfaces of the housing and of the seal parts.

To achieve this result, the invention provides a threepiece sealassembly with a trapezoidal main part sweeping the peripheral housing,and a pair of end pieces likewise substantially trapezoidal in form, buthaving surfaces sweeping both a side wall and a portion of theperipheral housing, and mating with the main part along an inclinedplane. Further, the inner surface of the peripheral housing is formed ofa harder material than the inner faces of the side walls, and the middlepiece of the seal assembly is formed of a harder material than the endpieces. By this means the wear of the individual parts is systematicallycorrelated so as to maintain good sealing and fit throughout all engineconditions, as will be explained in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an axial cross-section of anengine, showing the hard facing of the peripheral housing and an apexseal assembly in place; and

FIG. 2 is a fragmentary cross-section showing the position of the sealparts at installation.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a rotary combustionengine 1 having a peripheral housing 2 and side walls 3 and 4, whichtogether define an internal cavity 5. A generally polygonal,multi-apexed rotor 6 is rotatably mounted within the cavity on aneccentric portion 7 of a shaft 8 which transpierces the end walls. Therotor 6 is provided at each apex with an axially-extending groove 9, inwhich is disposed an apex seal assembly 10, comprising a trapezoidalmiddle part 11 and two smaller trapezoidal end parts 12. The positioningof the seal parts is such that the longest edge of the middle part 1 1sweeps along the inner peripheral surface 13, while the end parts 12have their shortest edges sweeping the peripheral surface 13 and theirend edges, at to their shortest edges, sweeping the inner faces 14 ofthe side walls 3 and 4. The middle seal part and the end parts meetalong sloping edges 16 disposed at an angle to the longitudinal axis ofthe shaft.

A leaf spring 15 is disposed in the groove 9 under the seal assembly,with its ends bearing against the undersides of the end parts 12 andurging them radially outward, whereby through the wedging action of theoblique abutment surfaces 16 between the middle part and the end partsthere occurs a simultaneous pressing of the middle part 11 against theinner peripheral surface 13 and of the end parts 12 against the inner.faces 14 of the side walls 3 and 4.

The peripheral housing 2 is provided with an inner coating layer 13 ofhard material, as for instance a deposit of nickel containing adistribution of 2 to 8 percent silicon carbide particles having anaverage grain size of approximately 1 micron. This material is harderthan the inner faces 14 of the side walls, which may be of nitridedhardened cast iron.

The middle part 1 l of the apex seal is harder than the end parts 12,the middle part having a Vickers hardness (l0 kilogram load) of at least600 and preferably of more than 1,000, and the end pans having ahardness of 300 to 500.

The material for the middle part consists of an iron alloy containing atleast 30 percent by weight of titani um carbide, and the end parts areformed of a cast iron alloy of the type used for piston rings. Nominalcompositions for suitable alloy materials for the middle seal part areasfollows.

EXAMPLE I Titanium carbide 34.5% Nickel 0.2 Carbon 0.55 Molybdenum 2.0Chromium 6.5 Iron Balance EXAMPLE II Titanium carbide 33% Nickel 15Molybdenum 5 Cobalt 9 Titanium 0.7

Aluminum 0.7 Copper 0.5 Iron Balance The Vickers hardness of the alloyof Example I amounts to approximately 1,030 to 1,090, and the hardnessof the alloy of Example 11 amounts to approximately 700 to 750.

The material of the end parts of the seal strip may be a cast iron alloyhaving the nominal composition given below, with a Vickers hardness ofapproximately 350 to 450.

EXAMPLE III Carbon 3.4 3.8% Silicon 2.5 3.2 Molybdenum 0.8 1.3 ManganeseChromium Vanadium less than 1% each Copper Nickel lron Balance FIG. 2shows the method of installing the seal assembly. At installation, onlythe end parts 12 are pressed by the spring against the inner peripheralsurface 13, with the main seal piece 11 resting between them against theslanted edges 16. The gap between the main seal piece and the surface13, however, is much exaggerated in the drawing for clarity ofillustration. Because the end parts are formed of a relatively softmaterial compared to the inner peripheral surface, in operation theirshort edges rapidly wear down to the height of the middle part 11, sothat after a short run-in period the condition shown in FIG. 1 isreached, in which the middle part and the end parts bear against theperipheral surface 13 across its entire width, while the end partscontinue to maintain sealing abutment against the side walls.

With the arrangement described, and the proper hardness relationsbetween the various parts, the seal assembly will continue to run trueand maintain good sealing over a long period of time. The hard materialof the main seal piece 11 wears very slowly, and the end parts 12 beingsofter they will always wear to at least the same amount and thus notprotrude, with the danger of abrading the housing. Further, since theend parts have only a small bearing portion against the peripheralhousing, the major part of seal wear is taken up by the center piece,and the end parts will not wear to a lower level and leave a gap.

What is claimed is:

l. A rotary internal combustion engine having a peripheral housing and apair of side housings defining an internal cavity and a rotor rotatablymounted within the cavity, the rotor having a plurality of apex portionswith a sealing arrangement positioned in a slot at each apex portion tosweep the inner surface of the peripheral housing and the inner faces ofthe side housings in sealing relationship, wherein the improvementcomprises:

a. The inner peripheral surface being formed of a harder material thanthe inner faces of the side housings;

b. each sealing arrangement comprising a middle part and two end parts;the middle seal part being generally trapezoidal and having a longsidedisposed radially outwardly and sweeping t e inner peripheral surface, a

shorter side parallel with the long side and disposed radially inwardly,and two short ends slanting from the long side to the shorter side;

. the two end parts each being generally trapezoidal and having a shortside disposed radially outwardly and sweeping the inner peripheralsurface, a longer side parallel with the shorter side and disposedradially inwardly, one end perpendicular to the short side and to thelong side and sweeping the adjacent side housing, and an opposite endslanting from the short side to the longer side and juxtaposed in matingrelationship to the slanting end of the middle seal part in such amanner that the sealing assembly of the three seal parts has a generallyrectangular outline;

. the middle seal part being formed of a harder material than the endseal parts but less hard than the inner peripheral surface of thehousing;

f. the end seal parts being urged resiliently outwardly and exerting awedging action outwardly against the middle seal part to maintain theradially outward edges of the three seal parts in sealing contactwiththe inner peripheral surface with seal wear thereagainst beingpreferentially absorbed by the end seal parts.

2. The combination recited in claim 1, wherein the inner peripheralsurface is formed of a layer of nickel having hard particlesincorporated therein, the middle seal part consists of a material havinga Vickers hardness of at least 600, and the seal end parts consist of amaterial having a Vickers hardness of at least 300.

3. The combination recited in claim 2, wherein the nickel layer hasincorporated therein from 2 to 8 percent of silicon carbide particleshaving an average particle size of approximately 1 micron.

4. The combination recited in claim 3, wherein the middle seal partconsists of an iron alloy containing at least 30 percent titaniumcarbide, and the end seal parts consist of piston-ring cast iron.

5. The combination recited in claim 4, wherein the end seal parts areformed of an alloy consisting of 3.4 to 3.8 percent carbon; 2.5 to 3.2percent silicon; 0.8 to 1.3 percent molybdenum; less than 1 percent eachof manganese, chromium, vanadium, copper, and nickel; and the balanceiron, the alloy having a Vickers hardness of at least 350.

6. The combination recited in claim 5, wherein the middle seal part isformed of an alloy having the nominal composition of 34.5 percenttitanium carbide, 0.2 percent nickel, 0.55 percent carbon, 2 percentmolybdenum, 6.5 percent chromium, and the balance iron, the alloy havinga Vickers hardness over 1,000.

7. The combination recited in claim 5, wherein the middle seal part isformed of an alloy having the nominal composition of 33 percent titaniumcarbide, 15 percent nickel, 5 percent molybdenum, 9 percent cobalt, 0.7percent titanium, 0.7 percent aluminum, 0.5 percent copper, and thebalance iron, the alloy having a l l 4 4' I

1. A rotary internal combustion engine having a peripheral housing and apair of side housings defining an internal cavity and a rotor rotatablymounted within the cavity, the rotor having a plurality of apex portionswith a sealing arrangement positioned in a slot at each apex portion tosweep the inner surface of the peripheral housing and the inner faces ofthe side housings in sealing relationship, wherein the improvementcomprises: a. The inner peripheral surface being formed of a hardermaterial than the inner faces of the side housings; b. each sealingarrangement comprising a middle part and two end parts; c. the middleseal part being generally trapezoidal and having a long side disposedradially outwardly and sweeping the inner peripheral surface, a shorterside parallel with the long side and disposed radially inwardly, and twoshort ends slanting from the long side to the shorter side; d. the twoend parts each being generally trapezoidal and having a short sidedisposed radially outwardly and sweeping the inner peripheral surface, alonger side parallel with the shorter side and disposed radiallyinwardly, one end perpendicular to the short side and to the long sideand sweeping the adjacent side housing, and an opposite end slantingfrom the short side to the longer side and juxtaposed in matingrelationship to the slanting end of the middle seal part in such amanner that the sealing assembly of the three seal parts has a generallyrectangular outline; e. the middle seal part being formed of a hardermaterial than the end seal parts but less hard than the inner peripheralsurface of the housing; f. the end seal parts being urged resilientlyoutwardly and exerting a wedging action outwardly against the middleseal part to maintain the radially outward edges of the three seal partsin sealing contact with the inner peripheral surface with seal wearthereagainst being preferentially absorbed by the end seal parts.
 2. Thecombination recited in claim 1, wherein the inner peripheral surface isformed of a layer of nickel having hard particles incorporated therein,the middle seal part consists of a material having a Vickers hardness ofat least 600, and the seal end parts consist of a material having aVickers hardness of at least
 300. 3. The combination recited in claim 2,wherein the nickel layer has incorporated therein from 2 to 8 percent ofsilicon carbide particles having an average particle size ofapproximately 1 micron.
 4. The combination recited in claim 3, whereinthe middle seal part consists of an iron alloy containing at least 30percent titanium carbide, and the end seal parts consist of piston-ringcast iron.
 5. The combination recited in claim 4, wherein the end sealparts are formed of an alloy consisting of 3.4 to 3.8 percent carbon;2.5 to 3.2 percent silicon; 0.8 to 1.3 percent molybdenum; less than 1percent each of manganese, chromium, vanadium, copper, and nickel; andthe balance iron, the alloy having a Vickers hardness of at least 350.6. The combination recited in claim 5, wherein the middle seal part isformed of an alloy having the nominal composition of 34.5 percenttitanium carbide, 0.2 percent nickel, 0.55 percent carbon, 2 percentmolybdenum, 6.5 percent chromium, and the balance iron, the alloy havinga Vickers hardness over 1,000.
 7. The combination recited in claim 5,wherein the middle seal part is formed of an alloy having the nominalcomposition of 33 percent titanium carbide, 15 percent nickel, 5 percentmolybdenum, 9 percent cobalt, 0.7 percent titanium, 0.7 percentaluminum, 0.5 percent copper, and the balance iron, the alloy having aVickers hardness of at least 700.